The present invention is to be understood in light of what has previously been done in the field. However, the following discussion is not an acknowledgment or admission that any of the material referred to was published, used or part of the common general knowledge in Australia as at the priority date of the application.
Immunoglobulin A (IgA) is the dominant immunoglobulin in human secretions, including breast milk and provides the body with protection against pathogens, binding to disease-causing viruses, bacteria, fungi and their toxins. IgA provides infants essential protection against the aforementioned pathogens. IgA antibodies are effective when taken orally because they are resistant to degradation by enzymes in the gut, thus making them ideal as nutraceuticals or food supplements. IgA may be combined with probiotics to inhibit or reduce adverse effects due to pathogens. Applications include use of IgA as a nutraceutical ingredient to target pathogens which cause infections of human mucosal surfaces such as in the nose, eyes, ears, lungs, breast and vagina. Moreover, IgA-containing products are suitable for gut and oral health applications. Due to the low levels of IgA normally present in cows' milk, the established method to increase the yield of IgA on a commercial scale is by immunisation regimes to boost the levels in the milk. Typically, cow's milk contains IgA and IgG in a ratio of approximately 1:8.
Compositions containing IgA for food consumption are currently produced globally, using essentially the same process and in virtually the same manner. The most common production methodology is referred to as a hyperimmunisation process whereby generally a number of cows are administered an immunogenic substance such as a virus to produce a hyperimmune response. As a consequence of the hyperimmune response, milk produced by the immunised cows contains increased amounts of IgA, otherwise known as “hyperimmune milk”. The hyperimmune milk is then concentrated using standard membrane technology to produce a milk product extract containing around 5% w/w IgA, which can be used as a food supplement such as for infant milk formula.
An inherent problem with the procedure to produce the hyperimmune milk is that it generally takes up to three months for the immunisation regime to generate a hyperimmune response in the cows and then a further month to harvest the hyperimmune milk in sufficient quantities to produce a commercial amount of IgA-containing milk product extract. Additionally, this procedure is also expensive compared to the process of the present invention.
IgA has an acidic isoelectric point, or pI, in the range of approximately 4.5-6.5 due to variable glycosylation, and is not generally considered to be able to adsorb to cation exchange resins in an amount that would be of commercial value. The process of the present invention surprisingly allows for the fractionation of IgA from milk products such as skim milk by cation exchange chromatography by modifying the loading and elution conditions. Such a process has not previously been achieved on a commercial scale.
Moreover, the process of the present invention may be included as part of an existing process for purification of other components of milk products, such as lactoferrin, lactoperoxidase or growth factors. An example of such a process is one where milk product is contacted with the cation exchange resin and an IgA-enriched fraction is eluted first, followed by an IgA-depleted lactoperoxidase fraction and then a lactoferrin fraction by sequential elution with mobile phases of increasing ionic strength.